The mechanisms by which oral streptococci interact with teeth, saliva, and with each other to form cariogenic dental plaque are under investigation. Human or rat saliva depresses the adsorption of S. mutans serotype b and c cells to hydroxyapatite. Both types of saliva cause aggregation of only serotype c cells and appear to favor the adsorption of type c cells to hydroxyapatite. A rapid quantitative method to screen substances with a cariogenic potential has been developed. It measures growth, adherence and acid production by S. mutans. Mutants of S. mutans with diminished virulence and decreased ability to synthesize water-insoluble glucans adhered poorly to glass surfaces in the presence of sucrose. They were rendered as adherent as the parent strain following their exposure to glucosyltransferases that synthesized water-insoluble glucans. Human dental plaque formed in the presence of sucrose contained more lipoteichoic acid than plaques formed in the presence of glucose or xylitol. The importance of lipoteichoic acid in cariogenic dental plaque is being explored.